A differential housing supports a differential mechanism having gears that transmit torque from a transmission of a vehicle to axle shafts of the vehicle. Generally, bevels gears of the differential mechanism are housed in the differential housing. Alternatively, planetary gears can also be housed in the differential housing. The typical differential mechanism of the vehicle transmission is designed to transmit torque from a transmission output to the opposing axle shafts allowing right and left wheels to rotate at different speeds, particularly important when negotiating a turn. While performing generally the same function, differential mechanism have different dimensional requirements for rear wheel and front wheel drive vehicles. Specifically, differentials intended for use on the front wheel drive vehicles require a beveled and even annular shape in order to compensate for both the smaller packaging area available and to account for the steering characteristics of the front wheels of the vehicle.
Rear wheel drive vehicles are typically larger and require more torque production than the front wheel drive vehicles and include sport utility, pick-ups, and even heavy duty vehicles. Therefore, the rear wheel drive differential is typically dimensioned larger with heavier gauge steel than is a front wheel drive differential. Iron castings presently used to form a housing of a differential requires a large number of machining operations to produce finished parts having the dimensions necessary to provide adequate tolerances to support the gears disposed within the housing.
Given the high torque requirements that is typical of the rear wheel drive vehicle, it is believed that the differential housing should include a more dimensionally stable and durable configuration than what is required of a front wheel drive differential housing. Furthermore, many of the manufacturing drawbacks of cast differential housings have resulted in excessive cost of a typical vehicle transmission.
The art is replete with various designs of the differential housings and methods of forming the differential mechanisms, which are disclosed in the U.S. Pat. Nos. 6,045,479 to Victoria et al; 6,061,907 to Victoria et al; 6,176,152 to Victoria et al.; and 6,379,277 to Victoria et al. Each of the aforementioned United States Patents discloses a method of forming a differential housing using a cold flow-forming process. While the differential housing formed by the process disclosed in these prior art references are believed to be effective for use in a front wheel drive transmission, it is believed that the differential housings will not be as effective for use in a rear wheel drive vehicle. However, the dimensional improvements produced by the cold flow-forming process that enable sheet steel to be used to form the differential housing can also be used to form a differential housing for a rear wheel drive differential. Therefore, the cold flow-forming process disclosed in these prior art patents are included by reference herein.
The differential housings, as disclosed in the aforementioned prior art references, are formed from a single casting that is machined subsequent to casting. In particular, a housing portion is formed in a series of steps starting with a cup-shaped workpiece. The cup-shaped workpiece is fitted over a chuck and flow-formed into a housing preform. Operations such drilling and surface finishing are performed on the housing preform subsequent to the flow-forming process. Gears are placed in the differential housing and the housing is permanently sealed. After being sealed, the entire assembly cannot be serviced and must be replaced if one of the internal components fails.
There is a constant need in the area of differential housings, formed by the cold flow-forming process and by forging and the like, for an improved design of the differential housing that is easily disassembled and is easily serviceable in a short period of time, particularly when one or more of the gears need to be replaced without having to replace the entire differential housing.